1. Field of the Invention
The present invention relates to a universal joint, and more particularly to a universal joint which may be used with a power or manually-operated tool to deliver force in an offset manner to a fastener or other workpiece.
2. Description of Prior Art
The universal joint makes access possible where straight access (0° offset) is difficult or impossible. A very common use of such a device is removing and replacing difficult to access fasteners on an automobile. The universal joint must transmit a primarily rotational force imparted by a manual or power driver to a socket or drive tang through a variable range of angular offset. Additionally, the universal joint must hold its position against gravity to allow ease of placement.
Typically the universal joint design has used a “pin and ball” design as the common design (U.S. Pat. No. 2,441,1347 to Dodge). In the “pin and ball” design the impact load is transmitted via the shear and bearing strength of the pin and ball. The failure mode of this device is typically the shearing of the pin with an occasional neck failure. Additionally the bearing area where the pin contacts the slot within the ball becomes deformed because of the great amount of force and lack of material support. The deformation of the ball results in premature binding of the joint. The friction device of this design is typically a conical coil spring that loses its force through repeated over-compression during use.
A more recent design (described in U.S. Pat. No. 4,188,801, Hugh et al) uses a quadrified ball in a square socket. Hugh et al design doesn't have the shear problem of the “pin and ball” design. However, it has to be larger than competing products which limits its usefulness and has a movability issue. The large size is the result of how torque and impact forces are transmitted in a largely radial manner extending outward and thereby requiring significant material thickness to support a given torque or impact event. Movability of this configuration is not smooth near its full deflection angle when the product is new. After a few impact cycles the movement of this joint becomes worse since the corners of the quadrified ball become deformed and begin binding on the interior of the square and the retaining ring.
In U.S. Pat. No. 4,824,418 Taubert discloses an articulated joint for coupling shafts that pivot with respect to each other. The joint has a cylindrical hollow drive element and a spherical drive element. The hollow drive element is shaped like a hollow cylinder with a wavy inner profiling and the spherical drive element has a spherical shape with a wavy profiling complementary thereto. Even on pivoting the shafts with respect to one another, there is a positive connection and a reliable force transfer during rotation. No lugs are disclosed in the hollow drive element.
A quadrified ball is formed on a driven member received in a cavity in a driving member as disclosed by Reynolds in U.S. Pat. No. 5,851,151. The quadrified ball rests on a plug tension washer which contacts the head of the ball and presses the ball against a C spring. A polymeric member is adjacent to the ball
In U.S. Pat. No. 6,152,826, Profeta describes a product that is “. . . substantially a sphere with spaced-apart lugs extending outwardly, formed around a circumference of the sphere.”. These lugs interact with “channels” to drive the mating component. The Profeta design addresses many of the issues found in Dodge and in Hugh et al; i.e., there is no single pin to shear or slot to weaken the ball as in Dodge and unlike Hugh et al the forces are primarily tangential which allows for a smaller more useful outer diameter of product.
However, the Profeta design is incapable of achieving a competitive range of motion while maintaining required strength and assembly integrity. The possible range of motion (angular offset) in this product is proportional to the ratio of sphere diameter to neck diameter. Therefore, for greater angular deflection, it is required to increase the sphere diameter or decrease the neck diameter. The maximum spherical diameter is limited by the minimum length of lugs that extend outward from the sphere, minimum outer wall thickness and maximum outer diameter of the mating part. The minimum neck diameter is limited by strength requirements. Assembly integrity is associated with how and where the sphere is contained within the assembly.
If the neck were made large enough to enable competitive torque strength while maintaining an acceptable overall size, than the angle of deflection would be insufficient to be competitive. If range of motion were made competitive, then torque strength would suffer. Attempts to bring both range of motion and torque strength to competitive standards results in insufficient spherical contact to insure a reliable assembly.